[llvm] [DAGCombiner] Attempt to fold 'add' nodes to funnel-shift or rotate (PR #125612)

[Justin Fargnoli via llvm-commits]

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@@ -8379,7 +8383,7 @@ static bool matchRotateSub(SDValue Pos, SDValue Neg, unsigned EltSize,
   // NOTE: We can only do this when matching operations which won't modify the
   // least Log2(EltSize) significant bits and not a general funnel shift.
   unsigned MaskLoBits = 0;
-  if (IsRotate && isPowerOf2_64(EltSize)) {
+  if (IsRotate && !FromAdd && isPowerOf2_64(EltSize)) {
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justinfargnoli wrote:

Is it incorrect to do this for `add`? Or do we just not want to? 

https://github.com/llvm/llvm-project/pull/125612